EXTENDED-RANGE STRUCTURAL CORRELATIONS IN AMORPHOUS SOLIDS

Extended-range order (ERO), extending beyond 35 Angstrom, has been discovered in very large (> 10 000 atom) structural models of a-Si. These weak, but quasi-periodic, atomic-density fluctuations have a period of R similar or equal to 3.4 Angstrom, which corresponds to the position of the first sharp diffraction peak (FSDP) in the structure factor of a-Si at Q similar or equal to 1.9 Angstrom(-1). In fact, more than half of the FSDP intensity is associated with the ERO fluctuations for r greater than or equal to 10 Angstrom. Atomic-void-based correlations are as well defined as atom correlations at large distances: the FSDP is equivalently found to be a chemical-order prepeak in S-proportional to(Q) in the Bhatia-Thornton formalism calculated for the atom-void packing, thereby supporting the void model for the origin of the FSDP.